1. Field of the Invention
The present invention relates to a light source for a display apparatus and a method for driving the light source.
2. Description of the Related Art
In general, liquid crystal display (LCD) apparatuses are thin, light and have low power consumption, which makes them popular for large television screens, monitors, notebook computers, cellular phones, etc. An LCD apparatus includes an image display panel utilizing the electro-optically controlled light transmittance of liquid crystals and a backlight assembly providing light to the display panel.
The backlight assembly includes a light source generating light to display an image on the display panel. The backlight assembly may apply a cold cathode fluorescent lamp (CCFL) or light-emitting diodes (LED). Nowadays, the backlight assembly mainly employs LEDs instead of CCFL, because LEDs have low power consumption and high color reproducibility.
The display LEDs include a red LED, a green LED and a blue LED. Red, green and blue light generated from the red, green and blue LEDs are mixed into white light. However, the luminance of the LEDs changes according to their usage time, temperature and humidity.
FIG. 1 is a graph illustrating a relationship between the lifetime and luminance of LEDs.
Referring to FIG. 1, LEDs have different luminance characteristics and lifetime depending on LED's color. The lifetime of a red LED is the shortest among the three color LEDs.
The backlight assembly compensates for LED luminance variation to achieve accurate color reproducibility. In a prior art, a backlight assembly detects an amount of light generated by red, green and blue LEDs using color sensors. Then, the backlight assembly adjusts the luminance by comparing the amount of the light detected with the target color coordinates and target luminance, and then optimizing a driving signal to the red, green and blue LEDs.
However, as the usage time of an LED increases, its luminance decreases and the backlight assembly may not be able to match the target white color coordinates and the target luminance.